Well, these are ways to describe the way in which the Roman faction governs conquered provinces. Each faction has its own method of dealing with conquered provinces - this is just an example for Rome.

So, you conquer the province, you build the correct building for "support," and you get the bonuses and the ability to recruit certain (native) units.

We may or may not have similar buildings for the Italian peninsula, I am not sure what we'll be doing about the Samnite, Apulian, Campanian, and other regional units there yet.